Why are Allergies More Common in Developed Countries?

Allergies are a type of inappropriate immune response, where our bodies misidentify a harmless substance as a threat.For a long time, we've been aware that allergies occur much more frequently in Western countries, but we don't know why this is. One idea that has grown in popularity is the hygiene hypothesis, which suggests that our immune systems need to come into contact with a range of micro-organisms when we are young to be able to produce appropriate immune responses later in life.

Researchers have discovered a molecular mechanism that could explain why allergies are less common in developing countries. Writing in the journal, Immunology, they report that this finding could be the first step to developing new immunotherapies to prevent allergies.

Lead author Dr Joseph Igetei, formally of the University of Nottingham, UK, now at the University of Benin, Nigeria, said, "We know that worm infections occur more frequently in less developed countries, i.e. in places where allergies are rare. Although it's been suggested that worm infections could prevent against different allergies, there has been little concrete evidence of the potential molecular mechanisms that might mediate any such relationship."

In this study, the research team led by Professor Mike Doenhoff from the University of Nottingham, and including Dr Joseph Igetei, Dr Marwa El-Faham from Alexandria University and Dr Susan Liddell, set out to discover if the antigens produced by a common species of parasitic worm that infects humans (called Schistosoma mansoni) were cross-reactive to antigens from peanuts, i.e. do the proteins from the worm and from the peanuts trigger the same immune response?

To investigate this, they used antibodies from rabbits that had been exposed to various life stages of the worm - antibodies are a type of immune protein made by the body to provide a tailored response to any substance deemed to be a threat. The researchers tested if these antibodies (which had been produced specifically against the parasitic worm) also reacted to various proteins found in peanuts.

They found that the antibodies responded to several proteins in the peanut, in particular one called Ara h 1, which is known to be a key player in inducing the negative response in people who are allergic to peanuts.

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"It may sound strange that peanuts and worms have anything in common that could cause the immune system to generate the same response," said Professor Mike Doenhoff. "However, our work indicates that proteins from these two seemingly very different organisms actually have identical markers on them, meaning the immune system views them in the same way and targets them with similar antibodies."

These findings are important in two ways. Firstly, this work goes some way to explaining the molecular mechanisms behind the observation that countries with a high incidence of worm infections have a low incidence of allergy. Although more work is needed to confirm the exact relationship, the team think that antibodies produced in response to a worm infection could stop the immune system from producing an allergic reaction when faced with a novel substance such as peanut protein.

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Secondly, this work may lead to new ideas to treat allergies. The team's next step is, however, to see if antibodies produced by humans in response to a worm infection also cross-react with peanut proteins.

Source-Eurekalert